NAIROBI , Kenya , July 03, 2008 (AP) — More than 20,000 Africans have crossed the Gulf of Aden to Yemen this year, paying brutal smugglers who cram them into boats and often throw the weakest overboard, an aid group said Thursday.

The number of migrants who reached Yemen has doubled from the same period last year, according to Medecins Sans Frontieres, also known as Doctors Without Borders. About 400 migrants have been confirmed dead or missing through the end of May.

"Smugglers operating in the Gulf of Aden are notorious for their brutality and take advantage of the extreme vulnerability of the refugees and migrants," the group said in a report. "Abuses are the rule, not the exception."

Migrants from the Horn of Africa — particularly from Somalia , where ongoing violence has killed thousands of civilians — regularly face abuse at the hands of smugglers. Some are attacked during the journey and thrown overboard into shark-infested waters. Smugglers often force passengers to disembark offshore to avoid Yemeni coast guard patrols.

Waves of migrants leaving West Africa for Europe make similarly perilous journeys.

The high season for smuggling across the Gulf usually runs from September to May, when the sea is less stormy than during summer. Yemen has increased coastal patrols, forcing smugglers to make the journey by night, increasing the risk.

Often, smugglers who hope to make a quick escape from nighttime security forces will "drop people in the middle of the ocean," said Javier Fernandez, the MSF head of mission for Somalia .

"The ones who are able to swim, they don't know where the shore is," he said. "The others drown."

MSF also said it has documented cases where smugglers beat people whose children were crying, threw people overboard and forced people to sit on top of each other in storage holds.

But the migrants, most of whom come from Somalia , see escape as their only option for survival.

Somalia has not had a functioning government since clan-based warlords toppled dictator Mohamed Siad Barre in 1991. The warlords then turned on each other, sinking the poverty-stricken nation of 7 million people into chaos. The weak government, backed by Ethiopian troops, is struggling to quash an insurgency that has killed thousands of civilians.

Thousands of Somalis, as well as Ethiopians, begin their journey in the Somali port city of Bossaso , hoping to reach Yemen and the richer Gulf countries beyond.

The route from Bossaso to Yemen is also a well-known arms smuggling route.

Yemen , one of the poorest Arab countries, is struggling with the refugee influx.

" Yemen is facing a major dilemma, particularly because of the continuous influx of African asylum seekers," Vice President Abd Rabu Mansour said in a speech this week in the capital San'a. "The international community needs to find speedy solutions for the Somali crisis."